The present invention relates to an optical compensation film, an optical compensation film support, a viewing angle compensation integral type polarizing plate, and a liquid crystal display apparatus.
Currently, cellulose acetate film (represented by cellulose triacetate film) is widely employed to prepare silver halide light-sensitive photographic materials as well as optical films due to its desirable characteristics such as high transparency as well as minimal optical drawbacks. Particularly, cellulose acetate film is preferably employed as a polarizing plate protective film for liquid crystal display apparatuses.
Incidentally, when images on a crystal liquid display apparatus are viewed from an oblique direction, image quality is degraded compared to that when viewed directly from the front. The resulting image degradation is due to viewing angle characteristics inherent in liquid crystal display apparatuses. In order overcome this drawback, an effective method is known in which viewing angle compensation film is arranged between the liquid crystal cell and the polarizer (refer, for example, to Japanese Patent Publication Open to Public Inspection Nos. 2000-154201 and 2002-156527).
However, it has been found that problems are not completely solved employing the aforesaid method.
(Patent Document 1)
Japanese Patent Publication Open to Public Inspection No. 2000-154201
(Patent Document 2)
Japanese Patent Publication Open to Public Inspection No. 2002-156527
The inventors of the present invention conducted investigations in an attempt to solve the aforesaid problems. As a result, Japanese Patent Application No. 2002-322923 was submitted. The patent application discloses markedly effective techniques described below. In the viewing angle compensation integral type polarizing plate, stated in the specification of the aforesaid patent, an appropriate phase difference compensation function is given to a polarizing plate protective film. Consequently, the production process is abbreviated to allow the viewing angle compensation film to adhere to the polarizing plate. As a result, it is possible to simplify the production process and to decrease the thickness of liquid crystal display apparatuses. However, in the aforesaid invention, since film is oriented in the transverse (td) direction (or lateral direction), residual strain remains. The aforesaid residual strain results in dimensional variation during storage. As a result, in practice, critical problems have occurred in which the polarizing plate, adhered onto the liquid crystal cell, peels off.
In order to overcome the aforesaid problems, a method is considered in which physical dimensional variation is minimized, for example, by increasing the adhesion force of an adhesive which adheres a liquid crystal cell to a polarizing plate. This technique minimizes physical dimensional variation, but the film is apparently in a state of orientation or contraction, resulting in a state in which stress is applied to the film. The resulting stress varies the retardation of the film and markedly affects viewing angle compensation characteristics during storage. As a result, in view of durability of the viewing angle characteristics, critical problems have practically occurred.